Is Your Sunscreen Messing With Your Sperm?

by Brittany Smith & Men's Fitness Editors

You want your sunscreen to filter and block out UV rays. You don’t want your sunscreen messing with your sperm. And you definitely don’t want the chemicals to mimic the effect of progesterone (yes, the female hormone) in your body. But, certain ones could potentially do just that, according to a new Danish study.

Before you throw away all of your SPF and swear off the stuff, know that more research is needed to confirm a link between human fertility and sunscreen chemicals. Not only do you need sunscreen to protect your skin from skin cancer (just ask Hugh Jackman!), it’s also key to keeping your skin looking young. And there are “safer” options out there.

Based just on what we know from this study, certain chemicals in certain sunscreens can interfere with sperm function, but we don’t know for sure whether that has any impact on fertility. “We see effects on sperm cells in vitro, but we don’t know if these effects somehow affect the in vivo ability to achieve successful fertilization,” study author Anders Rehfeld, MD, told us in an email. Now, the study is pretty science-y so if you’re just interested in the bottom line, click to page three. Otherwise, click to the next page for all the nitty gritty details.

The Science: First, a quick primer on how sunscreen works—and the root of the problem: Chemical UV filters absorb the harmful rays, reducing how much UV gets absorbed in your skin. When you smear sunscreen on, the chemicals are soaked up almost immediately. Some UV filter chemicals have even, reportedly, been found in human blood samples as well as 95 percent of urine samples in the U.S. and abroad, according to the study’s press release. Naturally, researchers were curious if this could harm our health.

So, scientists from the University of Copenhagen and Copenhagen University Hospital tested 29 of the 31 UV filters (more on these in a bit) allowed in sunscreens throughout the U.S. (or the European Union) on live healthy human sperm cells. The sperm samples, obtained from several donors, underwent testing in a buffer solution resembling conditions in female fallopian tubes. Stay with us.

The team tracked the sperm cells’ calcium signaling (movement of calcium ions brought on by changes in their concentration), which plays a major role in their function and well-being. More specifically, they looked at movement in the sperm-specific calcium ion channel called CatSper; it’s crucial to male fertility and the main sperm receptor for progesterone—the female hormone that attracts sperm cells. When everything’s working optimally, progesterone will bind to CatSper and cause a surge of calcium ions into the sperm cell in the hopes of fertilization. Still with us?

The researchers discovered 13 of the 29 UV filters tested sparked a surge of calcium ions in the sperm cells that interfered with normal sperm cell function. What’s more, nine of the 13 UV filters mimicked the effect of progesterone by activating the CatSper channel, also causing an influx of calcium ions. Essentially, these UV filters may act as endocrine disruptors.

What You Need to KnowAgain, no need to freak out just yet until we have more science backing up these results. But, if you’re worried, you can replace your chemical sunscreen with a physical one: “I would recommend using sunscreens with physical UV filters instead, and get the protection without the possible side-effects,” Rehfeld told us. Physical UV filters include zinc oxide and titanium dioxide which are minerals found naturally in the environment, according to the Wall Street Journal. Here are three physical sunscreens recommended by our Style and Grooming editor Barret Wertz:

In general, “look for “Physical” or “Mineral” on the package,” says Wertz. “Often “Sensitive Skin” sunscreens are more likely to use physical- or mineral-based sunscreens since the chemicals can sometimes cause rashes or breakouts.”